Lagging vs Leading Strand
DNA replication is an important biological process occurs in all living organisms with regards to their inheritance. In the process of replication, double helix of DNA molecule is unzipped, and each strand acts as a template for the daughter strand so that, the bases are matched in order to synthesize the new partner strands. As a result of this process, two identical copies of the molecule are produced. The DNA replication takes place at the “replication fork” created by helicase enzyme, which is responsible to break hydrogen bonds connecting the two DNA strands together. The resulting single DNA strands serve as templates for the newly synthesized DNA strands called “lagging and leading strands”.
Lagging strand is one of the two newly synthesized DNA strands in DNA replication. It is synthesized in the direction away from the replication fork. The synthesis of new strand of replication DNA in lagging strand is by the creation of short segments of various lengths called “Okazaki fragments”. Enzyme called DNA-ligase is responsible to join these fragments together. Therefore, the activity of DNA-ligase enzyme is essential for the synthesis of lagging strand.
Leading strand is the other newly created DNA strand that is being replicated continuously, unlike the lagging strand. Therefore, DNA-ligase activity is not required for the synthesis of this leading strand and needed to be primed only once. This strand is made in the 5’ to 3’ direction in which replication fork is moving.
What is the difference between Lagging and Leading Strand?
• Leading strand template is facing a 5’ to 3’ direction, whereas lagging strand template is oriented in 3’ to 5’ direction.
• Unlike lagging strand, leading strand is synthesized continuously during the replication process.
• The generation of Okazaki fragments can be found only in the lagging strand synthesis, whereas they cannot be found in leading strand synthesis.
• DNA- ligase is not required for leading strand synthesis, whereas it is required for lagging strand synthesis.
• The direction of synthesis of leading strand is 5’→3’ while that of lagging strand is 3’→5’ direction.
• DNA replication on the leading strand needs to be primed only once, whereas lagging strand synthesis requires new primers often to accommodate repetitive initiation events.
• Primase is responsible to synthesize the multiple RNA primers for the lagging strand, whereas RNA polymerase is required to synthesize leading strand.
• The replication of the lagging strand is more complicated than that of the leading strand though they are synthesized simultaneously.